1. Field of the Invention
This invention relates to a rolling method of H-shaped steels, and more particularly to a method wherein a web height of the wide flange beam is freely and precisely adjusted without requiring rearrangement of rolls to obtain an H-shaped steel having a constant outer width (web height).
2. Related Art Statement
In general, H-shaped steels are manufactured by hot rolling a starting workpiece 1, 2 or 3 as shown in FIGS. 2a to 2c through a line combining a breakdown rolling mill 6 with a rough universal rolling mill 7, an edger rolling mill 8 and a finish universal rolling mill 9 as shown in FIGS. 1a and 1b.
That is, each starting workpiece shown in FIGS. 2a to 2c (numeral 1 is a slab, numeral 2 a bloom, and numeral 3 a beam blank) is first roughened into a given shape in the breakdown rolling mill 6. As this mill 6 is used a 2-high breakdown rolling mill having upper and lower rolls engraved into an opening pass 4 or a closed pass 5 as shown in FIGS. 3a and 3b.
In brief, the workpiece is processed into a shape suitable for subsequent middle stage rolling by using various shaped calibers in the breakdown rolling mill 6 and successively rolling the workpiece through plural passes therein.
The roughened workpiece is subjected to a rolling at one pass or plural passes through the rough universal rolling mill 7 having one or more roll stands of a roll form as shown in FIG. 4a and the edger rolling mill 8 having one or more roll stands of a roll form as shown in FIG. 4b, which is then rolled into an H-shaped steel product at one pass through the finish universal rolling mill 9 having a roll form as shown in FIG. 4c. Therefore, when the product size is determined, the width of horizontal roll size of the finish universal rolling mill 9 as well as the width of horizontal roll of the former rolling mills are naturally determined.
That is, it is designed to make a size w1 in FIG. 3a, and sizes w2, w3 and w4 in FIGS. 4a to 4c substantially equal to each other.
Thus, the change of shape after the breakdown rolling is particularly restricted in the rolling of H-shaped steel. In case of rolling workpieces into H-shaped steels of particular size series (e.g. H600.times.300 or the like), therefore, a horizontal roll having a particular width is usually used.
However, the following problem is caused according to the conventional rolling method using the above horizontal rolls having such a particular width.
In H-shaped steels rolled by the horizontal roll of particular width, the web inner width is constant. When H-shaped steels of one size series are manufactured by using workpieces having a scattered flange thickness through the above horizontal roll, since the width of the horizontal roll is constant, the roll distance between the horizontal roll and the vertical roll is changed in accordance with the flange thickness. For example, in case of H-shaped steel having an ordinary size, the difference of flange thickness between maximum value and minimum value is about 16 mm at each flange portion, so that the web height is naturally changed within a range of about 32 mm.
Such a change of web height in the same size series is not avoided in the conventional rolling technique. When such a conventional rolling technique is applied to the manufacture of H-shaped steels for use in buildings, there is caused the following serious problem. That is, when a building beam is formed by joining plural H-shaped steels rolled in the same size series, since the web height is different even in the same size series as mentioned above, a large divergence at the joint face between the adjoining H shaped steels is caused, which comes into problem in the execution.
Further, when the structure of the building is designed in the usual manner, the size is successively determined from the outside toward the inside. On the other hand, the web height in the rolled H-shaped steels may be different though the web inner width is constant. The latter case considerably comes into problem when the severeness is required in the scramble to other size at the operating place.
Moreover, the rolled H-shaped steel has a problem in the size accuracy.
That is, in the rolling of H-shaped steel, a side face 11 of a horizontal roll 10 in the rough universal rolling mill 7 is worn as the rolling number increases to gradually reduce the roll width of the horizontal roll 10 as shown in FIG. 5. And also, a vertical roll 12 is worn together with the horizontal roll 10, but problems brought due to the wearing of the vertical roll are solved by merely adjusting the roll gap.
On the contrary, as to the wearing of the horizontal roll, when the rolling is carried out at a constant flange thickness t as shown in FIG. 6, not only the web inner width w5 but also the web height h reduce by the worn amount of the side face 11 of the horizontal roll 10. Therefore, the web height h is usually ensured by thickening the flange thickness t within a dimensional tolerance.
However, such a dimensional tolerance is as very small as .+-.3.0 mm when the web height is less than 400 mm, .+-.4.0 mm when the web height is not less than 400 mm but less than 600 mm, and .+-.5.0 mm when the web height is not less than 600 mm as defined according to JIS G3192. Since the web height h of the workpiece is dependent upon the size of the width of horizontal roll, the effective roll width of the horizontal roll usually used within the dimensional tolerance of the web height is restricted.
As mentioned above, when the rolling is continued by using the horizontal roll having a roll width reduced due to the wearing in the same size series, the flange thickness and hence the web height of the resulting product naturally change, so that it is required to replace the worn horizontal roll with new rolls. Furthermore, when the rolling is continued by using the new horizontal roll, the scattering of the flange thickness and hence web height in the products before and after the replacement of the new horizontal roll is naturally caused.
Since the above problem is caused when the web height in the H-shaped steel products obtained by the conventional rolling is not constant, H-shaped steels produced by welding plates so as to make the web height constant are used as a material for building. In the latter case, the production cost becomes naturally and undesirably high as compared with the case of the rolled H-shaped steel.
As the conventional technique, there are some techniques as disclosed, for example, in Japanese Patent laid open No. 59-133902, No. 60-82201, No. 61-262404 and the like.
In the technique disclosed in Japanese Patent laid open No. 59-133902, a width variable roll capable of changing a position in axial direction is incorporated into each of the rough universal rolling mill 7, the edger rolling mill 8 and the finish universal rolling mill 9 as shown in FIG. 1a to conduct partial rolling of web and rolling of flange end portion, whereby the rolling for difference web heights can be conducted by the same roll. Furthermore, in the technique disclosed in Japanese Patent laid open No. 60-82201, a sectional roll capable of changing a position in axial direction is incorporated into each of the primary rough universal rolling mill 7a, the edger rolling mill 8, the secondary rough rolling mill 7b and the finish rolling mill 9 as shown in FIG. 1b, whereby the rolling for different web heights and flange widths can be conducted by the same roll, or the above sectional roll is incorporated into each of the primary rough universal rolling mill 7a, the secondary rough universal rolling mill 7b and the finish rolling mill 9, whereby the rolling for different web heights can be conducted by the same rolling chance.
According to these techniques, since the web height can be varied within a large range, workpieces of several size series can be continuously rolled, so that the above techniques have many effects such as reduction of roll exchange number and the like as compared with the conventional rolling. However, when the web height of all products is made constant in the same size series, in spite that the adjusting amount of the distance between the sectional rolls is about 30 mm, a pair of horizontal rolls each comprised of two sectional rolls movable in the axial direction are arranged in each of the rough universal rolling mill, the edger rolling mill and the finish universal rolling mill, so that the equipment cost becomes very vast.
On the other hand, in the technique disclosed in Japanese Patent laid open No. 61-262404, when the workpiece after the breakdown rolling is hot rolled through rough rolling, finish rolling and the like into an H-shaped steel, it is first subjected to the rough rolling so as to form protrusions on both end portions of the web and then the finish rolling is carried out by using a pair of horizontal rolls each comprised of at least two sectional rolls capable of changing the position of the roll in the axial direction every rolling pass and properly changing the position of the sectional roll. In this method, however, the web protrusions having a thin thickness and a low temperature is partly rolled in the finish rolling step, so that there is still a problem of applying an over load to the sectional roll due to the increase of the roll surface pressure.